Polio Paralyzes 2 Children in West Ukraine Outbreak

Two children in western Ukraine have been paralyzed by polio, in the first cases of the disease seen in Europe in five years, the World Health Organization announced Wednesday.

Although the infections are a setback in the global drive against polio, the W.H.O.’s director of polio eradication, Dr. Hamid Jafari, said that the outbreak appeared to be small and that similar ones had been quickly snuffed out.

The two children, an infant and a 4-year-old, were not paralyzed by the “wild-type virus” that is now known to be circulating only in Pakistan and Afghanistan, but by a strain derived from the oral polio vaccine itself.

The oral vaccine contains three strains of weakened live virus, and very occasionally — the W.H.O. estimates it as once in a million vaccinations — one mutates to become more virulent. Then, like wild virus, it can be shed in feces and spread to others in sewage.

Outbreaks of vaccine-derived virus are usually limited and can be stopped by immunizing children in areas around all known cases. Ukraine has a large supply of polio vaccine on hand and is preparing a vaccination drive, Dr. Jafari said.

The two new cases occurred in villages only about 30 miles apart, and sewage sampling suggests the outbreak is not widespread. Polio thrives in hot weather, and Ukraine’s cold winter should slow any spread.

The challenge, Dr. Jafari said, is that half of Ukraine’s children are not fully immunized against polio and many other diseases.

That shortfall is not related to the struggles with Russia in the eastern part of the country, he said. The outbreak is in the west, near the borders with Romania, Slovakia, Hungary and Poland.

Rather, many Ukrainian parents resist vaccines because of a 2008 case in which a high school student died, apparently of sepsis, shortly after getting a shot for measles, mumps and rubella.

The Health Ministry and the United Nations Children’s Fund, which supplied the vaccine, insisted then that the death was a coincidence and that the vaccine was safe. But panic spread, and nearly 100 students went to hospitals complaining of headaches, fevers and sore throats.

The president at the time, Viktor A. Yushchenko, ordered all measles immunizations halted while officials investigated. Since then, about a third of Ukrainian parents have told pollsters that they fear vaccines, and vaccination rates have plummeted.

The incidence of measles rose from 100 cases in 2010 to 12,700 two years later. In 2013, Unicef warned that Ukraine was at risk of a polio outbreak.